Paper-feeding apparatus and image-forming apparatus

ABSTRACT

A paper-feeding apparatus includes a double paper feed prevention mechanism including a conveyance roller rotating forward in a paper feeding direction, and a handling roller rotating rearward in an opposite direction to the paper feeding direction through a torque limiter and being driven by the conveyance roller when the number of fed sheets of paper is one, a double paper feed detection sensor disposed at a downstream side of the double paper feed prevention mechanism to detect a physical quantity corresponding to the number of fed sheets of paper, and a control unit that determines a frequency of double paper feed events at the downstream side of the double paper feed prevention mechanism based on an output signal of the double paper feed detection sensor, and controls a speed of rearward rotation of the handling roller depending on the frequency of the double paper feed events.

BACKGROUND OF THE DISCLOSURE

The present applicant claims the benefit of priority of Japanese Patent Application No. 2011-144104 filed on Jun. 29, 2011, the content of which is incorporated herein by reference.

FIELD OF THE DISCLOSURE

The present application relates to a paper-feeding apparatus and an image-forming apparatus.

DESCRIPTION OF RELATED ART

Generally, an image-forming apparatus such as a copying machine, a printer, a multi-functional machine or the like includes a paper-feeding apparatus that feeds paper accommodated within a paper accommodation unit sheet-by-sheet. Such a paper-feeding apparatus is constructed to send out a sheaf of paper sheet-by-sheet into a paper conveyance path from the uppermost sheet to the lowermost sheet by a paper feed roller (also called a pickup roller) rotating in a feeding direction of the paper while being in press contact with a top face of the sheaf of paper. During this send-out operation of the paper, a plurality of paper may be sent out to the paper conveyance path at a single time. Such an event is hereinafter called “a double paper feed.”

One approach to solve this problem is as follows. When the paper sent out from a paper-feeding cassette into the paper conveyance path by the pickup roller reaches a predetermined position on the paper conveyance path by a conveyance roller, the conveyance roller is controlled to rotate in an opposite direction to the paper feeding direction so as to return paper subsequent to a second sheet of paper conveyed in an overlapped manner with a first sheet of paper to the paper-feeding cassette, thereby preventing the double paper feed.

A conventional paper-feeding apparatus may include a double paper feed prevention mechanism having a conveyance roller disposed at a downstream side of the paper feed roller and rotating forward in the feeding direction of the paper and a handling roller having a rotation shaft coupled to a torque limiter while facing the conveyance roller. The torque limiter is set such that the handling roller is driven by the conveyance roller when the number of sheets of paper interposed between the conveyance roller and the handling roller is one, whereas the handling roller stops (or rotates rearward when rearward rotation torque is applied) when the number of sheets of paper interposed between the conveyance roller and the handling roller is two or more.

In this manner, when the number of sheets of paper sent out on the paper conveyance path by the conveyance roller is one, the handling roller is driven by the conveyance roller, so that the paper is conveyed to a downstream side in the paper feeding direction (downstream side along the paper conveyance path) normally. On the other hand, when the number of sheets of paper sent out on the paper conveyance path by the conveyance roller is two or more, the handling roller stops (or rotates rearward), so that a first sheet of paper closer to the conveyance roller is conveyed to a downstream side in the paper feeding direction normally, while sheets of paper subsequent to a second sheet of paper closer to the handling roller stop at their positions (or return to an upstream side of the paper feeding direction). In this way, the double paper feed may be prevented.

However, the above-mentioned double paper feed prevention mechanism may not prevent the double paper feed with a 100% success rate. For this reason, one conventionally known configuration is that a double paper feed detection sensor is disposed at a downstream side of the double paper feed prevention mechanism to detect a physical quantity related to a paper thickness. Using this configuration, when the double paper feed event is detected based on an output signal of the double paper feed detection sensor, a paper jam error is generated. In response to the paper jam error notification, a user is requested to deal with the paper jam error or the paper is forcedly discharged out, thereby interrupting the image-forming process. Consequently, working performance of the user can be deteriorated.

SUMMARY

An object of the present disclosure is to suppress a frequency of a double paper feed event, thereby improving working performance of a user.

In accordance with one aspect of the present disclosure, a paper-feeding apparatus is provided including a double paper feed prevention mechanism including a conveyance roller rotating forward in a paper feeding direction, and a handling roller rotating rearward in an opposite direction to the paper feeding direction through a torque limiter and being driven by the conveyance roller when the number of fed paper sheets is one, a double paper feed detection sensor disposed at a downstream side of the double paper feed prevention mechanism to detect a physical quantity corresponding to the number of fed paper sheets, and a control unit that determines a frequency of double paper feed events at the downstream side of the double paper feed prevention mechanism based on an output signal of the double paper feed detection sensor, and controls a speed of rearward rotation of the handling roller depending on the frequency of the double paper feed events.

In accordance with the present disclosure, for example, when the frequency of double paper feed events is high, the speed of rearward rotation of the handling roller is controlled to decrease, thereby improving a success rate of the double paper feed prevention by the double paper feed prevention mechanism. In this way, it is possible to suppress the frequency of the double paper feed events, thereby improving working performance of a user.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a configuration of a multi-functional machine A according to one embodiment of the present disclosure;

FIG. 2 schematically shows a configuration of a paper-feeding apparatus included in the multi-functional machine A;

FIG. 3 is a flow chart illustrating a control sequence of a paper-feeding operation carried out by a control unit 6; and

FIG. 4 is one example of table data showing a corresponding relationship between the number of double paper feed events and the number of paper feed events, which is recorded in an embedded RAM of the control unit 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Moreover, a multi-functional machine having functions of copying, printing, scanning, faxing and the like will be described as an example of an image-forming apparatus according to the present disclosure.

FIG. 1 schematically shows a configuration of a multi-functional machine A according to this embodiment. As shown in FIG. 1, the multi-functional machine A may include an operation display unit 1, an image-reading unit 2, an image data storage unit 3, a paper conveyance image-forming unit 4, a communication unit 5 and a control unit 6.

The operation display unit 1 may have an operation key and/or a touch panel and thus serve as a human-machine interface to connect a user and the multi-functional machine A to each other. The operation display unit 1 may output an operation instruction corresponding to the operation key that is pressed and/or an operation button displayed on the touch panel to the control unit 6. Moreover, the operation display unit 1 may display various pictures through the touch panel based on a control signal input from the control unit 6.

Under the control of the control unit 6, the image-reading unit 2 may read a surface image (a document image) of a document automatically fed by an auto document feeder (ADF) or a document disposed on a platen glass using line sensors, and then may convert the surface image into document image data which in turn is output to the control unit 6. The image-reading unit 2 outputs the document image data to the control unit 6, and the control unit 6 stores the document image data in the image data storage unit 3. The image data storage unit 3 may be a semiconductor memory, a hard-disk device or the like. The image data storage unit 3 may store the document image data, print image data sent to the communication unit 5 from an external client computer (not shown), facsimile image data sent to the communication unit 5 from a facsimile apparatus and the like, based on a control signal input from the control unit 6. Under the control of the control unit 6, the paper conveyance image-forming unit 4 may convey paper sheet-by-sheet from a sheaf of paper accommodated within a paper-feeding cassette 44 and then form an image on the conveyed paper based on the image data stored in the image data storage unit 3. Such a paper conveyance image-forming unit 4 may include, as shown in FIG. 1, a plurality of image-forming units 41 to form an image (hereinafter, called “a toner image”) made of toners corresponding to 4 colors of black, yellow, cyan and magenta, an intermediate transfer belt 42, primary transfer rollers 43, the paper-feeding cassette 44, a paper-feeding roller 45, a double paper feed prevention mechanism 46, a double paper feed detection sensor 47, resist rollers 48, a secondary transfer roller 49, fixing rollers 50, a paper discharge roller 51 and a paper discharge tray 52.

Each of the image-forming units 41 forms respective toner images corresponding to black, yellow, cyan and magenta respectively, and thus 4 image-forming units corresponding to the four colors respectively are horizontally installed at a predetermined interval when seen from a front of the multi-functional machine A. Each of the image-forming units 41 may have, as shown in FIG. 1, a photo-sensitive drum 41 a having a corresponding toner image formed at a peripheral face thereof.

The intermediate transfer belt 42 may be an endless belt installed to be in contact with each photo-sensitive drum 41 a. The corresponding toner image formed at the peripheral face of each photo-sensitive drum 41 a is primarily transferred therefrom to the intermediate transfer belt 42. Each primary transfer roller 43 is arranged to face a corresponding photo-sensitive drum 41 a while the intermediate transfer belt 42 is interposed therebetween. The corresponding toner image may be primarily transferred from each photo-sensitive drum 41 a to the intermediate transfer belt 42 by applying a primary transfer voltage to the intermediate transfer belt 42 while rotating each primary transfer roller 43.

The paper-feeding cassette 44 may be a container to accommodate a sheaf of paper PS with a given size such as A4, B5 or the like. The paper-feeding cassette 44 has an opening for exposing at least a top surface of the sheaf of paper PS.

As shown in FIG. 2, the paper-feeding roller 45 sends the paper P from an uppermost portion of the sheaf of paper PS along a paper conveyance path L sheet-by-sheet via forward rotation in a paper-feeding direction in a pressure-contact state with the exposed top surface of the sheaf of paper PS within the paper-feeding cassette 44. Here, the paper-feeding direction refers to a direction (as indicated by an arrow in the figure) of the conveyance of the paper P along the paper conveyance path L.

In addition, a rotation drive mechanism (a motor, a decelerating gear or the like) not shown in the figure is coupled to a rotation shaft of the paper-feeding roller 45. The forward rotation motion (a starting time, a stopping time, a speed or the like of the forward rotation) may be controlled via control of the rotation drive mechanism (in particular, to application of forward rotation torque by control of the motor) by the control unit 6.

The double paper feed prevention mechanism 46 is disposed at a downstream side of the paper-feeding roller 45 along the paper conveyance path L (that is, downstream side in the paper feeding direction). The double paper feed prevention mechanism 46 prevents the double paper feed by separating a first sheet of a paper P from underlying sheets of paper P including a second sheet of a paper when a plurality of sheets of paper P are sent to the paper conveyance path L by the paper-feeding roller 45 at a single time, in other words, when the double paper feed occurs.

To be specific, the double paper feed prevention mechanism 46, as shown in FIG. 2, includes a conveyance roller 46 a rotating forward in the feeding direction of the paper, and a handling roller 46 b rotating rearward in an opposite direction to the feeding direction of the paper through a torque limiter not shown in the figure while facing the conveyance roller 46 a and at the same time being in pressure contact with the conveyance roller 46 a. A rotation drive mechanism (a motor, a decelerating gear or the like) not shown in the figure is coupled to a rotation shaft of the conveyance roller 46 a. The forward rotation motion (a starting time, a stopping time, a speed or the like of the forward rotation) of the conveyance roller 46 a may be controlled via control of the rotation drive mechanism (in particular, application of forward rotation torque by control of the motor) by the control unit 6. In addition, for the double paper feed prevention mechanism 46, rotation force of the paper-feeding roller 45 may be transferred to the rotation shaft of the conveyance roller 46 a via a belt.

A rotation drive mechanism (a motor, a decelerating gear or the like) not shown in the figure is coupled to a rotation shaft of the handling roller 46 b through a torque limiter not shown in the figure. The rearward rotation motion (a starting time, a stopping time, a speed or the like of the rearward rotation) of the handling roller 46 b may be controlled via to control of the rotation drive mechanism (in particular, application of rearward rotation torque by control of the motor) by the control unit 6. Here, the torque limiter for the handling roller 46 b is set in such a manner that, when one or zero sheets of paper are interposed between the conveyance roller 46 a and the handling roller 46 b, the rotation of the handling roller 46 b is driven by the rotation of the conveyance roller 46 a (See FIG. 2A). Otherwise, when two or more sheets of paper are interposed between the conveyance roller 46 a and the handling roller 46 b, the handling roller 46 b rotates rearward in an opposite direction to the feeding direction of the paper (See FIG. 2B).

The double paper feed detection sensor 47 detecting a physical quantity corresponding to the number of sheets of paper P is disposed at a downstream side of the double paper feed prevention mechanism 46 along the paper conveyance path L. The double paper feed detection sensor 47 includes an ultrasonic transmission unit 47 a and an ultrasonic reception unit 47 b which are arranged in a vertical manner and face each other with the paper conveyance path L interposed therebetween. The ultrasonic transmission unit 47 a sends an ultrasonic wave S upward toward the ultrasonic reception unit 47 b through the paper conveyance path L. The ultrasonic reception unit 47 b receives the ultrasonic wave S sent from the ultrasonic transmission unit 47 a and then outputs a voltage signal corresponding to reception intensity of the ultrasonic wave S to the control unit 6.

The reception intensity of the ultrasonic wave S of the ultrasonic reception unit 47 b has the highest level when the number of sheets of paper P moving toward a downstream side of the double paper feed prevention mechanism 46 is zero (namely, a no-feed state). The reception intensity of the ultrasonic wave S of the ultrasonic reception unit 47 b decreases as the number of sheets of paper P moving toward the downstream side of the double paper feed prevention mechanism 46 increases. That is, the reception intensity of the ultrasonic wave S of the ultrasonic reception unit 47 b may be a physical quantity varying depending on the number of sheets of paper P moving toward the downstream side of the double paper feed prevention mechanism 46. Therefore, the control unit 6 may determine, based on an output signal of the double paper feed detection sensor 47 (the ultrasonic reception unit 47 b), whether the number of sheets of paper P moving toward the downstream side of the double paper feed prevention mechanism 46 is zero (a no-feed state), one, or two or more.

To be specific, the control unit 6 may store the reception intensity of the ultrasonic wave S in the single paper feed state in advance as a reference intensity for comparison. The control unit 6 compares a reception intensity (an actual measurement value) derived from an output signal of the double paper feed detection sensor 47 (the ultrasonic reception unit 47 b) with the reference intensity. When the reception intensity and the reference intensity are equal, the control unit 6 determines that the number of sheets of paper P is one. When the reception intensity (the actual measurement value) is larger than the reference intensity, the control unit 6 determines that the number of sheets of paper P is zero. When the reception intensity (the actual measurement value) is smaller than the reference intensity, the control unit 6 determines that the number of sheets of paper P is two or more (a double-paper-feed state).

In addition, as long as it is possible to detect the physical quantity corresponding to the number of sheets of paper P, various types of sensors other than an ultrasonic type sensor or an optical type sensor may be employed as the double paper feed detection sensor 47.

Referring back to FIG. 1, a pair of resist rollers 48 are disposed at the downstream side of the double paper feed detection sensor 47 along the paper conveyance path L to adjust a timing when the paper P conveyed from the double paper feed prevention to mechanism 46 is conveyed toward the secondary transfer roller 49. The pair of resist rollers 48 include two rollers which rotate forward in the feeding direction of the paper while facing each other and being in press contact with each other.

The pair of resist rollers 48 are configured such that one roller thereof (a first roller) has a rotation shaft coupled to a rotation drive mechanism (a motor or a decelerating gear or the like) not shown in the figure while the other roller thereof (a second roller) runs idle. That is, the forward rotation motion (a starting time, a stopping time, a speed or the like of the forward rotation) of the first roller may be controlled via control of the rotation drive mechanism (in particular, application of forward rotation torque by control of the motor) by the control unit 6, whereas the rotation of the second roller may be driven by the rotation of the first roller.

The secondary transfer roller 49 is configured to face a back-up roller with the intermediate transfer belt 42 interposed therebetween. A secondary transfer nip portion is formed between the secondary transfer roller 49 and the intermediate transfer belt 42. Thus, the toner image on the intermediate transfer belt 42 is secondarily transferred to the paper P. That is, the secondary transfer roller 49 secondarily transfers the toner image on the intermediate transfer belt 42 to the paper P by applying a secondary transfer voltage in a state in which the paper P and the intermediate transfer belt 42 are interposed at the secondary transfer nip portion.

The fixing rollers 50 include a heating roller having a heater therein and a pressure roller in press contact with the heating roller. The fixing rollers 50 fix the toner image onto the paper by pressing and heating the paper P in a state in which the paper P having the secondary transferred toner image formed thereon via the secondary transfer roller 49 is interposed between the heating roller and the pressure roller. The paper discharge roller 51 discharges the paper P conveyed from the fixing rollers 50 into the paper discharge tray 52. The paper discharge tray 52 is a container in which the paper P discharged by the paper discharge roller 51 is received.

The communication unit 5 may communicate with an external multi-functional machine or facsimile apparatus over a telephone line or with a client computer over a LAN (local area network) or the like, depending on a control signal input from the control unit 6. That is, the communication unit 5 has both of a communication function in compliance with a LAN standard such as Ethernet (registered trademark) or the like and a communication function in compliance with a facsimile standard such as G3 or the like. The communication unit 5 may, for example, send e-mail or send/receive facsimile data.

The control unit 6 may include a CPU (Central Processing Unit), a ROM (Read-Only Memory), a RAM (Random Access Memory), an interface circuit for sending/receiving various signals to/from each of the above-mentioned components, and the like. The control unit 6 controls all operations of the multi-functional machine A based on a control program stored in the ROM.

All components of the present multi-functional machine A are described above. Among the above-mentioned components, the control unit 6, the paper-feeding cassette 44, the paper-feeding roller 45, the double paper feed prevention mechanism 46 and the double paper feed detection sensor 47 form a paper-feeding apparatus according to this embodiment. The image-forming unit 41, the intermediate transfer belt 42, the primary transfer roller 43 and the secondary transfer roller 49 function as toner image transfer units for transferring the toner image onto the paper P fed from the paper-feeding apparatus.

The fixing rollers 50 function as a fixing unit to fix the transferred toner image on the paper P. The paper discharge roller 51 and the paper discharge tray 52 function as paper discharge units for discharging the paper P having the fixed toner image formed thereon to the outside.

Hereinafter, an operation of the above-mentioned multi-functional machine A will be described.

For example, a user intending to copy a document using the multi-functional machine A initiates a copy operation of the multi-functional machine A by setting the document on the image-reading unit 2 and then pressing a copy start key of the operation display unit 1. In response to the pressing of the copy start key of the operation display unit 1 by the user, the control unit 6 enables the image-reading unit 2 to read a document image and stores document image data obtained from the image-reading unit 2 in the image data storage unit 3.

The control unit 6 controls each of the image-forming units 41 based on the document image data stored in the image data storage unit 3, to form (develop) the associated color toner images on the surfaces of the corresponding photo-sensitive drums 41 a respectively. The color toner images are sequentially and repeatedly transferred onto the intermediate transfer belt 42 by applying a primary transfer voltage to the primary transfer roller 43 while circulating the intermediate transfer belt 42.

The control unit 6 controls a paper-feeding operation of the paper P using the paper-feeding apparatus in parallel with the above-mentioned control of the primary transfer operation of the toner images. Hereinafter, a control sequence of the paper- feeding operation executed by the control unit 6 will be described in detail with reference to a flowchart as shown in FIG. 3.

As shown in FIG. 3, the control unit 6 counts up the number of paper feed events (increments a count value of the number of paper feed events) from the beginning of a paper-feeding operation (step S1). The sheets of paper begin to be conveyed (step S2). More specifically, the control unit 6 generates forward rotation torque by controlling the rotation drive mechanism for the paper-feeding roller 45 and the conveyance roller 46 a to to enable forward rotation of the paper-feeding roller 45 and the conveyance roller 46 a, and at the same time, generates rearward rotation torque by controlling the rotation drive mechanism for the handling roller 46 b to enable rearward rotation of the handling roller 46 b.

Here, as shown in FIG. 2A, when one sheet of a paper P from a sheaf of paper PS accommodated with the paper-feeding cassette 44 is sent out to the paper conveyance path L using the paper-feeding roller 45, the rotation of the handling roller 46 b is driven by the rotation of the conveyance roller 46 a, so that one sheet of paper P is conveyed to the downstream side of the double paper feed prevention mechanism 46 normally.

On the other hand, as shown in FIG. 2B, when two or more sheets of paper P (two sheets of paper P1 and P2 in FIG. 2B) from the sheaf of paper PS accommodated with the paper-feeding cassette 44 are sent out along the paper conveyance path L using the paper-feeding roller 45, the rotation of the handling roller 46 b is not driven by the rotation of the conveyance roller 46 a, but rearward rotation of the handling roller 46 b is enabled by the torque limiter. Thus, the first sheet of paper P1 closer to the conveyance roller 46 a is conveyed to the downstream side in the paper feeding direction via the forward rotation of the conveyance roller 46 a while the second sheet of paper P2 closer to the handling roller 46 b returns upstream in the paper feeding direction via the rearward rotation of the handling roller 46 b. In this way, it is possible to separate the first and second sheets of paper P1 and P2 from each other (that is, the double paper feed may be prevented).

However, frictional force between the first and second sheets of paper P1 and P2 may increase due to frictional force between the handling roller 46 b and the second sheet of paper P2. In this case, although two sheets of paper P1 and P2 are interposed between the conveyance roller 46 a and the handling roller 46 b, the rotation of the handling roller 46 b is driven by the conveyance roller 46 a. As a result, both of the first and second sheets of paper P1 and P2 may be conveyed to the downstream side of the double paper feed prevention mechanism 46.

For this reason, the control unit 6 determines whether the double paper feed event occurs or not at the downstream side of the double paper feed prevention mechanism 46, based on an output signal of the double paper feed detection sensor 47 (the ultrasonic reception unit 47 b) (step S3). Upon determining that the double paper feed event occurs at the downstream side of the double paper feed prevention mechanism 46 (“YES” in step S3 of FIG. 3), the control unit 6 counts the number of double paper feed events (increments the count value of the number of double paper feed events) (step S4). Moreover, the control unit 6 counts the number of paper feed events (a current count value of the number of paper feed events) from a previous double paper feed detection to a current double paper feed detection and records a relationship between the number of double paper feed events and the associated number of paper feed events in an embedded RAM (step S5).

That is, the embedded RAM of the control unit 6 includes table data showing the relationship between the number of double paper feed events and the number of paper feed events (the number of paper feed events from a previous double paper feed detection to a current double paper feed detection), as shown in FIG. 4. Then, the control unit 6 calculates a sum F of 5 previous numbers of paper feed events recorded in the RAM (step S6). For example, as shown in FIG. 4, when a current double paper feed is detected and a number of recent double paper feed events is “7,” the control unit 6 calculates the sum F of 5 previous numbers of paper feed events, that is, “30,” “13,” “35,” “26” and “18” corresponding to the numbers of double paper feed events “7,” “6,” “5,” “4” and “3” respectively, to obtain 122.

The resultant sum F of the numbers of paper feed events indicates total paper feed events until the double paper feed events not prevented from occurring using the double paper feed prevention mechanism 46 occur five times. Therefore, the larger sum F of the numbers of paper feed events indicates a low frequency of the double paper feed events whereas the smaller sum F of the numbers of paper feed events indicates a high frequency of the double paper feed events. That is, the sum F of the numbers of paper feed events itself serves as an indicator that indicates the frequency of the double paper feed events.

After calculating the sum F of the numbers of paper feed events as mentioned above, the control unit 6 carries out a count clear operation on the number of paper feed events (resets the count values of the number of paper feed events to zero) (step S7). The control unit 6 determines whether or not the sum F of the numbers of paper feed events is smaller than a first preset value FA (step S8). Upon determining that the sum F of the numbers of paper feed events is smaller than the first preset value FA (“YES” in the step S8 of FIG. 3), the control unit 6 determines that the frequency of the double paper feed events is high and then enables the speed of rearward rotation of the handling roller 46 b to be lower than an initial set value (step S9).

In this way, via the slow-down of the rearward rotation of the handling roller 46 b, the force to return the second sheet of paper P2 in an opposite direction to the paper feeding direction, as shown in FIG. 2B, may increase. That is, the frictional force between the handling roller 46 b and the second sheet of paper P2 may increase. Therefore, the improvement of the success rate of the double paper feed prevention using the double paper feed prevention mechanism 46 may be achieved.

On the other hand, upon determining that the sum F of the numbers of paper feed events is not smaller than the first preset value FA (“NO” in the step S8 of FIG. 3), the control unit 6 determines whether or not the sum F of the numbers of paper feed events is larger than a second preset value FB (step S10). Upon determining “YES” in step S10 of FIG. 3, in other words, when the sum F of the numbers of paper feed events is equal to or larger than the first preset value FA and is larger than the second preset value FB, the control unit 6 determines that the frequency of the double paper feed events is low and then enables the speed of rearward rotation of the handling roller 46 b to be higher (step S11). In this case, an upper limit of the speed of the rearward rotation is set to the initial set value.

Thereafter, after step S9 or step S11 or upon determining “NO” in step S10, the control unit 6 enables the paper P to be discharged to the paper discharge tray 52 without carrying out the image-forming operation on the paper P (in the case of the double-paper-feed state) (step S12). Further, upon determining “NO” in step S3, in other words, when one sheet of paper P is conveyed to the downstream side of the double paper feed prevention mechanism 46 as in a normal state, the control unit 6 allows the image-forming operation on the paper P (step S13) and then enables the paper P having the image formed thereon to be discharged to the paper discharge tray 52 (step S12).

In addition, the control unit 6 repeats the above-described steps 51 to S13 until all document image data read from the documents has been copied.

As described above, in accordance with this embodiment, the control unit determines the frequency of double paper feed events occurring at the downstream side of the double paper feed prevention mechanism 46 (the sum F of the numbers of paper feed events from several double paper feed detections before to a current double paper feed detection), based on the output signal of the double paper feed detection sensor 47 (the ultrasonic reception unit 47 b), and control the speed of rearward rotation of the handling roller 46 b depending on the frequency of the double paper feed events. Therefore, for example, when the frequency of double paper feed events is high, the speed of rearward rotation of the handling roller is controlled to decrease, thereby improving a success rate of the double paper feed prevention using the double paper feed prevention mechanism 46. In this way, it is possible to suppress the frequency of the double paper feed events, thereby improving working performance of a user.

Moreover, the present disclosure is not limited to the above-described embodiment but may have the following variations. For example, while the case of calculating the sum F of the 5 previous numbers of paper feed events is provided as an example in the above-mentioned embodiment, the numbers of paper feed events are not limited to 5. In addition, the number of paper feed events from a previous double paper feed detection to a current double paper feed detection may be taken as the frequency of double paper feed events.

When it is determined that the frequency of double paper feed events is high (“YES” in step S8 of FIG. 3), the speed of the rearward rotation of the handling roller 46 b may decrease step-by-step. When the speed of the rearward rotation of the handling roller 46 b is increased, this may be carried out step-by-step.

Although, in the above-mentioned embodiment, the multifunctional machine A is set forth as the image-forming apparatus including the present paper-feeding apparatus, the present paper-feeding apparatus may be applied to other types of image-forming apparatuses such as a copier, a printer, a scanner, a fax device, and the like.

Furthermore, although the paper-feeding apparatus that feeds paper P from the sheaf of paper PS accommodated in the paper-feeding cassette 44 is set forth as an example in the above-mentioned embodiment, an auto document feeder (ADF) that feeds document paper to be read sheet-by-sheet may also include the configuration as described above.

While preferred embodiments of the disclosure have been described and illustrated above, it should be understood that these are exemplary of the disclosure and are not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the scope of the present disclosure. Accordingly, the disclosure is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims. 

1. A paper-feeding apparatus comprising: a double paper feed prevention mechanism comprising a conveyance roller rotating forward in a paper feeding direction, and a handling roller rotating rearward in an opposite direction to the paper feeding direction through a torque limiter and being driven by the conveyance roller when the number of fed sheets of paper is one; a double paper feed detection sensor disposed at a downstream side of the double paper feed prevention mechanism to detect a physical quantity corresponding to the number of fed sheets of paper; and a control unit that determines a frequency of double paper feed events at the downstream side of the double paper feed prevention mechanism based on an output signal of the double paper feed detection sensor, and controls a speed of rearward rotation of the handling roller depending on the frequency of the double paper feed events.
 2. The paper-feeding apparatus of claim 1, wherein, upon detecting that a fed sheet of paper is in a double paper feed state at the downstream side of the double paper feed prevention mechanism based on an output signal of the double paper feed detection sensor, the control unit determines the number of paper feed events from a previous double paper feed detection to a current double paper feed detection as the frequency of double paper feed events.
 3. The paper-feeding apparatus of claim 1, wherein, upon detecting that a fed sheet of paper is in a double paper feed state at a downstream side of the double paper feed prevention mechanism based on an output signal of the double paper feed detection sensor, the control unit determines the total number of paper feed events from several double paper feed detections before to a current double paper feed detection as the frequency of double paper feed events.
 4. The paper-feeding apparatus of claim 2, wherein, when the number or the total number of paper feed events is smaller than a first preset value, the control unit determines that the frequency of the double paper feed events is high, and decreases the speed of rearward rotation of the handling roller.
 5. The paper-feeding apparatus of claim 3, wherein, when the number or the total number of paper feed events is smaller than a first preset value, the control unit determines that the frequency of the double paper feed events is high, and decreases the speed of rearward rotation of the handling roller.
 6. The paper-feeding apparatus of claim 4, wherein, when the number or the total number of paper feed events is equal to or larger than the first preset value and is larger than a second preset value, the control unit determines that the frequency of the double paper feed events is low, and increases the speed of rearward rotation of the handling roller.
 7. The paper-feeding apparatus of claim 5, wherein, when the number or the total number of paper feed events is equal to or larger than the first preset value and is larger than a second preset value, the control unit determines that the frequency of the double paper feed events is low, and increases the speed of rearward rotation of the handling roller.
 8. The paper-feeding apparatus of claim 2, wherein, upon detecting that the paper is in a double paper feed state, the control unit counts the number of double paper feed events and stores data indicating a corresponding relationship between the number of paper feed events and the number of double paper feed events in an embedded RAM.
 9. The paper-feeding apparatus of claim 3, wherein, upon detecting that the paper is in a double paper feed state, the control unit counts the number of double paper feed events and stores data indicating a corresponding relationship between the number of paper feed events and the number of double paper feed events in an embedded RAM.
 10. The paper-feeding apparatus of claim 4, wherein, whenever it is determined that the frequency of the double paper feed events is high, the control unit decreases the speed of rearward rotation of the handling roller step-by-step.
 11. The paper-feeding apparatus of claim 5, wherein, whenever it is determined that the frequency of the double paper feed events is high, the control unit decreases the speed of rearward rotation of the handling roller step-by-step.
 12. The paper-feeding apparatus of claim 6, wherein, whenever it is determined that the frequency of the double paper feed events is low, the control unit increases the speed of rearward rotation of the handling roller step-by-step.
 13. The paper-feeding apparatus of claim 7, wherein, whenever it is determined that the frequency of the double paper feed events is low, the control unit increases the speed of rearward rotation of the handling roller step-by-step.
 14. An image-forming apparatus comprising: the paper-feeding apparatus of claim 1; a toner image transfer unit that transfers a toner image on paper fed from the paper-feeding apparatus; a fixing unit that fixes the toner image transferred onto the paper; and a paper discharge unit that discharges the paper having the toner image fixed thereon to an outside. 